The present invention relates to a method for automatically removing and supplying needles in needle boards intended for the densification of fiber webs or non-woven fabrics into needle felts. The invention also relates to an apparatus with which this method can be implemented.
In the manufacture of needle felts made of fiber webs or non-woven fabrics, needle felt machines are employed to which the fiber web or non-woven material is fed horizontally as sheet material A needlebar is moved up and down vertically to the flat side of this sheet material on its upper and/or underside. This needlebar includes a receptacle, usually in the form of a slide guide, for a needle board. A plurality of needlebars may also be provided in succession in the direction of movement of the sheet material to accommodate successively acting needle boards, e.g. typically two such needlebars. The needle boards are provided with needle bores in a given pattern to receive the so-called felt needles which hereinafter will simply be called needles. Such needles typically have an angled portion, i.e. the trick, on the side of the needle board facing away from the sheet material which secures the needle against dropping through the needle bore and additionally absorbs the reaction pressure generated during the needle supplying process with respect to the needlebar From the one end of the trick, the so-called stem of the needle, usually in the form of a cylindrical rod, projects through the needle board and continues outside of the needle board on the side facing the sheet material in the form of a reduced shank and a needle-action end section which frequently is configured as a triangular structure ending in a point and equipped with grooves, notches or the like. Such needles are generally composed of a very brittle and thus breakage sensitive hardened metal, particularly certain steel alloys. The action of the needles in the fiber web or in the non-woven fabric densifies the latter more or less into a needle felt. With respect to details of the needling process, a needle felt machine and also typical needles employed in a needle board of the needlebar in a needle felt machine, reference is made, for example, to the monograph by Loffler, Dietrich and Flatt, entitled "Staubabscheidung mit Schlauchfiltern und Taschenfiltern" [Dust Removal by Means of Hose Filters and Pocket Filters] published by Vieweg-Verlag, Brunswick, 1984, ISBN 3-528-08566-5, pages 91-96.
Needle boards in use include a multitude of board geometries, board materials and board configurations. Older needle boards still in use are made of wood, particularly of laminated wood. Thereafter, the so-called sandwich structure was introduced in which a layer of rubber or a rubber substitute enclosed the needle stem in a friction lock and was boxed, e.g. by intermediate vulcanization, between two metal cover plates usually made of an aluminum-magnesium alloy. Recently, such three-layer sandwich structures have been formed of two-layer structures of a relatively thick metal plate, again usually an aluminum-magnesium alloy, and a thin plastic plate which is glued onto the side of the trick and now serves to hold the needle stem in a friction lock.
Depending on the manufacturer, the time of manufacture and the desired felt structure, the pattern of the needles in the individual needle boards, i.e. the pattern of the needle bores, varies in an unfathomable multitude. The most popular are the herringbone needle pattern and the random needle pattern. Although all of these needle patterns have in common that the needle pattern can be divided into imaginary rows along which the needles follow one another in a certain rhythm, it is impossible, particularly when including older needle boards, to speak of a certain given row spacing or certain distances between holes in the individual rows in an accurately preprogrammable manner. In the older needle boards, the distribution tolerances with respect to the spacing of the rows as well as the spaces between individual holes of one row are indefinite and relatively large Moreover, in the older needle boards there are needle bore deformations, particularly in their outwardly oriented end regions, often in a funnel-like shape with different tolerances in the connecting regions between these widened sections The already mentioned differences in board geometry may relate to their length, width, thickness and guide geometry of the needle board in the way it is accommodated in the needlebar. Additionally, it is sometimes customary to align the tricks in opposite directions in successive rows while in other cases they are all aligned in the same direction. Also, some needle bed manufacturers secure the tricks against rotation by providing continuous receiving grooves in the needle board in which the tricks are embedded so as to be flush with the remaining surface of the needle board. Instead, it is also known to simply embed the tricks without securing them against rotation in a flat recess on the surface on the side of the tricks so as to make them flush with respect to a projecting edge region. Otherwise, the tricks usually lie on a planar outer face of the needle board and correspondingly project relative to this outer face. Other differences in needle boards still in use may lie, for example, in the degree of aging of the needle board with respect to bending, increased tolerances in the needle bores after repeated replacement of needles and in their surface quality.
During operation of the needle felt machine, the needles are initially subjected to natural wear. Additionally, in an unpredictable manner, there occurs a more or less large amount of needle breakage so that an increasingly larger number of needles is no longer available for the needling process. For example, the triangular profile may break in the region of the needle tip or even the entire shank may break completely at a greater or lesser distance from the stem or the needle may be kinked or bent particularly in the region of the shank. As soon as a kinked needle or a needle which is bent into an oblique direction is unable to pass through the bores of the stripper plate disposed between the needle board and the sheet material being worked and/or through the perforated plate disposed behind the sheet material, it will finally be broken by one of these plates. However, needles which fail during operation increasingly worsen the quality of the produced needle felt.
Such needle destruction reduces their usability of the needle board substantially earlier than the set time at which, due to general wear, all needles should be replaced or a successive replacement of entire needle rows would be appropriate.
In the past, the replacement of individual destroyed needles has always been performed manually with machine or apparatus aids being employed for the manual activity To accomplish this, the maintenance person visually examines the needle board row by row. The remainders of individual destroyed needles in the needle bore are ejected and a respective new needle is inserted manually and then driven in. The above-mentioned machines or apparatus aids may be employed to eject and/or drive the needles in again. Ejection is effected either with a normal hammer equipped with an attachment for the needle or with a pneumatic hammer. Usually a normal hammer is employed for driving in the needle or also a device which facilitates the insertion of individual needles. An aid for the removal of needles is disclosed, for example, in DE-GM No. 1,912,670, aids for inserting needles are disclosed in DE-OS No. 1,265,426 and in DE-GM No. 83/29,050.8, particularly in its FIGS. 1 and 4.
In connection with a greater degree of automatization it has only become known to simultaneously and successively exchange whole rows of needles in a needle board. To do this, the respective needle row is ejected by means of an ejection strip which pushes out the needles or needle stumps still projecting on the working side of the needle board; an extraction strip is employed to extract the pushed-out needles on the other side, the side of the tricks, and a press-in strip for pressing new needles into the working position. However, between these steps, the needle board must be turned and the new needles must be manually inserted into the needle bores. This prior art method (see DE-GM No. 85/12,596.2 and DE-GM No. 1,923,665) therefore is only semiautomatic, insofar as the mode of operation of the mentioned individual strips is concerned and manual for turning the boards and preliminary re-insertion of new needles.
An even greater degree of automatization is known for a pure needle insertion process which is directed primarily to initially supply new needle boards with needles. Such methods and corresponding apparatus are therefore employed by the manufacturer of needle boards, but have not been accepted by the manufacturer of needle felts, particularly because the manufacturers of needle felts employ not only needle boards of a certain type but many types of different needle boards and many different hole distributions, particularly since the hole distribution can be changed by exchanging the respective needle board depending on the needle felt product desired.
Such needle insertion methods and the corresponding apparatus to be employed solely by the manufacturers of needle boards are disclosed in DE-OS No. 3,201,282 (corresponding to U.S. Pat. No. 4,568,010) and in DE-GM No. 83/29,050.8. Both processes have in common that new needles are supplied in a magazine and fed and driven in automatically. In particular, all individual, free needle bores in a row are actuated successively according to a numerical program control (DE-OS No. 3,201,282, page 13, paragraph 2) to thus equip all needle bores successively with needles. When the needles are put into the preliminary magazine, their tricks are positioned in a selected manner and the needles are then automatically supplied to the needle bores in the same or a modified trick position and are then driven into the bores. To precisely align the needles with the axis of the open bore hole, an opto-electronic receiver may be provided (DE-GM No. 83/29,050.8, page 9, penultimate paragraph) which beams into the open bore hole.
These prior art needle insertion methods and devices are hardly suitable or sometimes not suitable at all for supplying older needle boards with needles, whose original needles have already been removed, because in the older needle boards the tolerances of the needle bores change in an unpredictable manner. Moreover, the multitude of the needle boards at hand at a certain needle felt manufacturer's does not make possible without difficulty a precise numerical program control for the individual free needle bores of a certain needle board.
The above-mentioned difficulties were the reason that in the past no fully automatic process and the corresponding apparatus have become known neither for equipping needle boards with needles nor to remove the needles from a needle board. And no automatic process has been disclosed with which only individual damaged needles could be replaced with new needles.